There is widespread use of cars equipped with airbag devices for protecting occupants in the driver's seat and the passenger seat in a vehicle collision or in an emergency. The airbag devices are installed in, for example, the steering wheel and the instrument panel and have airbags that are inflatable and deployable. Furthermore, in recent years, knee-protecting airbag devices that can protect, at least, the knees of occupants are employed. In order to protect mainly the knees of the occupant, the airbag device is disposed in the vehicle body in front of the occupant, and the inflator is activated in a vehicle collision or in an emergency to inflate and deploy the airbag (a so-called knee bag or knee airbag) mainly between the vehicle body and the knees of the occupant.
This knee-protecting airbag device is disposed in, for example, a lower part of the instrument panel in front of the occupant. From there, in order to protect the occupant, the airbag is inflated and deployed toward a narrow space between the vehicle body and the occupant's legs up to the vicinity of the knees of the occupant before the knees of the occupant come into contact with the vehicle body. Therefore, knee-protecting airbag devices are required to have faster deployment characteristics, for example, the airbags need to deploy up to a height above the knees of the occupant within a short period of time (about 10 ms (milliseconds)) after the airbag starts to inflate and deploy. At the same time, if the airbag exerts a force in directions spreading the knees of the occupant apart during inflation and deployment, the injury to the occupant would be significant, which is dangerous. Therefore, the airbag is also required to deploy evenly on the left and right sides, while preventing the occupant from coming into contact with the airbag deploying in a lateral direction.
In order to meet such a requirement, conventionally, a knee-protecting airbag device is known in which the leading end in the airbag deploying direction is folded into the airbag to increase the deployment speed of the airbag, particularly on the leading end side, making it possible to protect the knees of the occupant and the vicinity thereof more appropriately (see Patent Document 1).
In this conventional knee-protecting airbag device, when the airbag is folded, an upper edge at the time of completion of inflation is folded into the airbag so as to be brought toward a lower edge, and the folded upper edge is then roll-folded so as to be brought toward the lower edge at a wall portion on the vehicle-body side. Then, the left and right ends that are roll-folded are folded back so as to be brought toward the center at a wall portion on the occupant side. By sequentially performing folding-in, roll-folding, and folding-back, the airbag is folded.
However, in this conventional knee-protecting airbag device, the airbag during inflation and deployment deploys only in reverse order to the folding order. That is, the above-described folding back portion, roll-folded portion, and folding-in portion of the upper edge are sequentially unfolded, and deployment is completed through these substantially three stages. Thus, this knee-protecting airbag device has a problem in that the deployment of the entire airbag is slow compared to a device having an airbag that deploys through fewer stages.
Furthermore, in this conventional airbag device, in the airbag in an initial stage of deployment, folded-back portions on both sides first open in the lateral direction and deploy in a direction substantially perpendicular to the upper direction where the knees of the occupant are positioned. Thus, deployment toward a position above the knees of the occupant is slow. As a result, in some cases, for example, in the case where the knees of the occupant are positioned closer to the front of the vehicle than usual and in the case where the moving speed thereof to the front of the vehicle is high, the protection function for protecting occupants may decrease. In addition, in this knee-protecting airbag device, the folding-back portions on both sides in the lateral direction, from where the deployment starts, are formed toward the occupant. Therefore, when the position where the folded airbag is attached to the vehicle body is close to the legs of the occupant, the folding-back portions on both sides, which deploy in the lateral direction, may come into contact with the knees of the occupant or the portions below the knees.
[Patent Document 1] Japanese Unexamined Patent Application, Publication No. 2005-271703